Testing Fuel pressure regulator

In the Rotax 912iS Installation Manual, Section 73–00–00, Page 12 provides the test procedure for the fuel pressure regulator. 

https://www.rotax-owner.com/en/support-topmenu/engine-manuals#current-engines

The fuel system must be checked during the first installation of the 912 iS engine. A single measurement of the fuel pressure, in reference to the intake manifold pressure at the inlet of the pressure regulator, is required by the engine manufacturer. Operating limits regarding fuel pressure must be observed under all operating conditions (e.g. engine load, temperature, altitude, filter contamination, etc.). For this measurement, a calibrated measuring tool must be used, and appropriate verification should be available from the aircraft manufacturer.

TIP: If the fuel pressure sensor is located at the inlet of the pressure regulator (see Position 1 Fuel Pressure Sensor in the interface overview, Figure 6.1), the limits in the Operator Manual 912 i Series (see Chapter 2.1, Section “Operating Limits”) must be complied with.

With the engine switched off (and both fuel pumps switched on), the pressure at the output of the fuel pressure regulator must not exceed 0.5 bar (7.25 psi) relative to ambient pressure. The minimum fuel pump pressure is 4.5 bar (65.26 psi) absolute at sea level.

Pressure Fluctuations: Fuel pressure regulators have precise tolerances and are generally reliable. Pressure fluctuations are typically not caused by the regulator itself, so troubleshooting should focus on other areas of the fuel system (e.g. clogged filters, line pulsation, kinks in hoses) before assuming the regulator is faulty.

The most current Fuel Pressure Regulator Inspection can be found in the Rotax 916iS Heavy Maintenance Manual, under Fuel Pressure Regulator Assembly Inspection, Section 73-10-00, Page 22. https://www.rotax-owner.com/en/support-topmenu/engine-manuals#current-engines

FUEL PRESSURE REGULATOR ASSEMBLY — INSPECTION

1. Check all the O-rings.

   NOTE:
   If an O-ring is damaged, the entire fuel pressure regulator must be replaced. O-rings are not available as spare parts.

2. Check the screen for dirt.

   NOTE:
   If the screen is dirty, check all pre-filters for function and contamination.

PRESSURE REGULATOR HOUSING — INSPECTION

1. Check the sealing surfaces of the O-rings for striations.

2. Check the recess of the retaining ring for sharp edges and burrs.

   NOTE:
   The depressions must not have sharp edges. Sharp edges can be carefully smoothed with a sharpening stone. The roughness of the flat surfaces must not be altered.

Thx, yes I have read the manual however that really doesn't help me much into troubleshooting into whether my regulator works as intended or opening at a too low pressure. I have normal fuel pressure during starting attempt, until it finally starts/ignite for a split second and immediately dies and at the same time as fuel pressures falls to zero for a second and then returns to normal.

The increased hissing sound can only (IMO) come from the fuel flow/line however no leaking fuel is visible.

If it was injectors being constantly open, I would assume it could start.

Any/all ideas are more than welcome.

Where is your fuel PSI sensor located in your fuel system? Is it attached to the fuel PSI regulator (P1), or is it located near the fuel filter on the inlet side of the fuel system (P2)?

Also, is your fuel filter positioned before or after the crossover bleed line (the crossover fuel line connects the inlet side of the fuel system to the return side)?

David Nyhjem wrote:

Thx, yes I have read the manual however that really doesn't help me much into troubleshooting into whether my regulator works as intended or opening at a too low pressure. I have normal fuel pressure during starting attempt, until it finally starts/ignite for a split second and immediately dies and at the same time as fuel pressures falls to zero for a second and then returns to normal.

The increased hissing sound can only (IMO) come from the fuel flow/line however no leaking fuel is visible.

If it was injectors being constantly open, I would assume it could start.

Any/all ideas are more than welcome.

You sure the vacuum hose going from the fuel pressure regulator into the air box is on tight with no leaks? 

Also, the fuel pressure regulator is a $20 Bosch part. See here: https://www.rotax-owner.com/en/912is-technical-questions/10562-fuel-pressure-regulator-400-from-rotax-or-22-online

The engine is on a Pipistrel SW if that is of any help. The fuel line is passed through the Rotax 874060 - Fuel Filter before entering into the (Andair) gascolator. The fuel pressure sender is located in the gascolator which also contains a 62m internal filter. The gascolator has a bypass valve. After this, it is split op to L & R. All filters are new. Hope it makes sense.